\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{circuitikz}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\ctikzset{bipoles/length=1cm}
\begin{document}
\small
\begin{circuitikz}[>=latex, scale=1.0,european]
  % \useasboundingbox(0.9,0)rectangle(5.1,5);
  \draw (-4,0)--(-2,0) to [rmeter, t=G] (0,0) to [R=$R$] (3,0)--(4,0);
  \node at (-4,0) [below]{$+$};
  \node at (4,0) [below]{$-$};
  \draw [->] (-4,0)--(-3,0) node [below]{$I_g$};
  \draw [dashed](-2,-1) rectangle (2.5,1);
  \node at (-.25,.3){$R_g$};
  \draw [fill=white](-4,0) circle (2pt);
  \draw [fill=white](4,0) circle (2pt);
\end{circuitikz}
\end{document}